Hot beverages such as coffee or cocoa are best enjoyed when consumed at a particular serving temperature range. A desired serving temperature usually cannot be maintained in the drinking cup, because the hot beverage is rapidly cooled by conduction heat transfer into the cup or other vessel and by convection to the surrounding atmosphere. Beverages served at drinking temperature soon cool to an unpalatable temperature, and beverages served at a hotter temperature can burn the drinker's mouth.
Insulated drinking vessels for liquid and semi-liquid foods are well known in the prior art. In the prior art, however, insulated vessels have included insulation surrounding the entire bottom and sides of the vessel. Thus, although such prior art insulated vessels act to retard loss and resulting cooling of liquid within the vessel, it is impossible to maintain the temperature of a liquid in the drinking vessel by using a surface heating unit such as a hot plate. The insulation on the bottom and side portions of prior art vessels would prevent heat from a hot plate from reaching the liquid within the vessel. Furthermore, some types of insulating material found on prior-art cups and other drinking vessels would melt on contact with a hot plate or other surface heat source.
Thus, a need has existed in the art for beverage cup apparatus capable of keeping a beverage warm, and also capable of transferring heat directly to the liquid contained therein from a surface-type heat source.